We will continue our studies of crystalline complexes of aspartate aminotransferase with L-glutamate, L-aspartate, Alpha-methylglutamate, Beta-hydroxyaspartate, phosphoserine, cysteic acid, and other amino acids. We will measure polarized light absorption spectra and determine equilibrium constants for the enzyme in the crystalline state. We will also diffuse substrates and inhibitors into preformed crystals and will ascertain the best conditions for determination of electron density difference maps by X-ray diffraction. Various analogs of pyridoxal-P will be used to replace the natural coenzyme in another series of esperiments. In this work we will collaborate closely with Dr. Arthur Arnone who is doing the X-ray crystallographic work and with Makinen of the University of Chicago. We will complete a study of the reactions of pyridoxal-5'-sulfate and of a vinylcarboxylic acid analog of pyridoxal-P with aspartate aminotransferase. We will attempt to learn the exact structures of the chromophoric peptides obtained by peptic digestion. A series of chemical investigations of glutamate decarboxylase from E. coli will be conducted. We hope to complete the proof of structure of a labile low molecular weight product formed by the reaction of serine sulfate and the enzyme. The band shapes of absorption spectra of pyridoxal phosphate-containing enzymes will be examined at both room temperature and low temperatures. Spectra will be fitted with lognormal curves and evidence for tautomerism will be sought. Special attention will be paid to enzyme-substrate complexes and to possible changes in vibrational fine structure.